streptococcus pneumoniae & viridans group of streptococci professor sudheer kher
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Streptococcus pneumoniae&
Viridans group of Streptococci
Professor Sudheer Kher
• S. pneumoniae• diplococci• Pneumococcus• autolysin• bile solubility test• optochin susceptibility• capsule• Quellung reaction• Inulin fermentation• Mouse pathogenecity
KEY WORDS
Viridans group of Streptococci
• Viridis = Green• Throat commensals, can cause opportunistic
infections.• ά - Haemolytic on blood agar.• Species – S. mitis, mutans, salivarius, sanguis.• Tooth extraction – Transient bacteremia leading to
implantation on damaged/prosthetic heart valves – Commonest species - sanguis.
• Dental caries - Commonest species – mutans.
S. pneumoniae
Important features
• Gram + , Lanciolate, capsulated diplococci
Important features• Aerobes & facultative anaerobes. Growth
improved by 5-10 % CO2
• Colonies on BA –ά - Haemolytic, dome shaped later showing flat and concentric ring pattern (carrom coin)
• Mucoid appearance
Important features
• Catalase & oxidase negative
• Bile soluble• Inulin fermentation• Optochin (ethyl
dihydrocuprein) sensitive
• Pathogenic to mice
Antigens
• Most important – Type specific capsular polysaccharide also called SSS (specific soluble substance). More than 90 serotypes detected.
• Typing methods –– Agglutination– Quellung reaction– Precipitation for SSS
S. pneumoniae • leading cause of pneumonia
– particularly young and old– after damage to upper respiratory tract
*e.g. following viral infection• bacteremia• meningitis• middle ear infections (otitis media)• Sinusitis, bronchitis, eye infections.
S. pneumoniae
• ά - hemolytic• pneumolysin
– degrades red blood cells under aerobic conditions
• grows well on sheep blood agar• no group antigen
Diagnosis - spinal fluid
• direct Gram staining• detection of capsular antigen
Autolysis - identification
Bile
peptidoglycan
cell membranelipoteichoic acid
teichoic acid-choline
autolysin
C polysaccharide
• Teichoic acid– Precipitates in serum– C-reactive protein – An abnormal protein (β-globulin)
that precipitates with somatic C antigen of pneumococci appears in acute phase sera in pnemonia and disappears in convalescence. Also occurs in many other pathological conditions. This is called CRP or acute phase protein.• Used to monitor response to treatment in various conditions
like rheumatic fever and is replacing ESR.
Not optochin sensitive
optochin sensitive
Identification
Capsule
• prominent – virulent strains
• anti-phagocytic• carbohydrate antigens
– vary among strains
Capsule
• immunity – serotype specific
• vaccine contains multiple serotypes• only for susceptible population
Quellung reaction
• using antisera • capsule "fixed" • visible microscopically
Pathogenesis
• Teichoic acid–complement activation –large numbers of inflammatory
cells at infection site
Therapy
• S. pneumoniae – most strains susceptible to
penicillin – resistance is uncommon but
known (5%)–Third generation of cephalosporin
or Vancomycin
Prophylaxis
• Polyvalent polysaccharide capsular antigens of 23 most common serotypes given to population at high risk– Absent/dysfunctional spleen– Sickle cell disease– Coeliac disease– Chronic renal/lung/heart/liver disease– NOT given to children < 2yrs, immunosuppression /
deficiency, lymphoreticular malignancy
Differences between Viridans Gp & Pneumococci
Point Pneumococci Viridans Gp
Morphology Capsulated, lanceolate, diplococci
Oval or rounded in chains
Quellung test + -
Colonies Dome shaped Draughtsman
Dome shaped
Growth in liquid Uniform turbidity Granular turbidity with powdery deposits
Bile solubility + -
Inulin fermentation + -
Optochin sensitivity + -
Intraperitoneal inoculation in mice
Fatal Infection Non-pathogenic
• S. pneumoniae• diplococci• Pneumococcus• autolysin• bile solubility test• optochin susceptibility• capsule• Quellung reaction• Innulin fermentation• Mouse pathogenecity
KEYWORDS